Animals have evolved a variety of sensory modalities in order to distinguish and respond to different cues in their environment. Taste, or gustation, is an essential component of an animal's chemosensory repertoire, affording it the ability to discriminate between noxious and nutritious substances and often eliciting specific behavioral responses. Much headway has been made in elucidating many of the specific G protein coupled receptors and subsequent transduction molecules involved in taste detection of sweet and bitter substances in mammals and flies. The molecular mechanism of salt taste, however, is unknown. Various ion channels have been proposed to mediate salt taste;however, evidence for involvement of specific genes remains elusive. In Drosophila, taste is mediated by gustatory neurons housed in sensory bristles that reside on the proboscis, legs, wings, internal mouthparts, and genitalia. There are 68 candidate Drosophila gustatory receptor genes that encode putative seven transmembrane domain G-protein coupled receptors (Scott K., Cell. 2001 Mar 9;104(5):661-73). These receptors detect sugars and bitter compounds, but whether they mediate the taste of salt or other substances is unknown. How does Drosophila detect salt? To investigate genes involved in Drosophila salt taste, a recent microarray-based screen was undertaken in order to identify taste-neuron specific genes. One identified gene, ppk23, a putative sodium ion-channel gene, is expressed specifically in candidate salt sensitive taste neurons. Additionally, preliminary electrophysiological data shows a specific salt taste defect in transposon mediated ppk23 hypomorphic mutant flies. The goal of this project is to test the hypothesis that ppk23 mediates salt taste detection in Drosophila. The first specific aim of the project is to determine the response properties of ppk23 via mis-expression and functional imaging analysis. The second specific aim is to determine the necessity of ppk23 in salt taste detection via mutant and functional imaging analysis. The third specific aim is to determine whether ppk23 mediates the behavioral response to both low and high salt. Millions of Americans suffer from hypertension, or high blood pressure. Moreover, dietary salt intake is implicated as a risk factor in development of this condition. Furthering understanding of the molecular mechanism of salt taste will undoubtedly aid in uncovering ways to prevent or manage this condition.